The present invention relates to a charged particle beam apparatus suitable for use as a micro fabrication (or processing) apparatus or a micro surface area analysis equipment using charged particle beams.
In techniques for processing or analysis of a micro area using an ion microprobe, it is indispensable to observe an image of a specimen surface for the purpose of determining a position on the specimen to be analyzed, etc. Conventionally, an optical microscope has been used as a tool for observing the image of the specimen surface. In recent years, however, in order to make it possible to observe even a micro or fine structure of a specimen surface which cannot be observed by the optical microscope, a method of observing the specimen surface by means of a finely focused electron beam has been proposed for an apparatus in which the micro area is processed or analyzed by use of the ion microprobe. In such a method, a charged particle source, a focusing lens and a deflector which form the ion microscope, are also used for forming an electron beam. Namely, since ions having positive charges and electrons having negative charges can take the same trajectory in principle by inverting the polarities of electric signals supplied to a source for generation of the ions and electrons (charged particle source), an electrostatic focusing lens, etc., the observation of an image of the specimen surface using the finely focused electron beam makes it possible to observe the specimen surface image as a scanning electron microscopy image having a resolution which is remarkably high as compared with the conventional method using the optical microscope. This type of apparatus is described in JP-B-51-5315.
By the prior art shown in the above-mentioned reference, it is possible to observe an image of a specimen surface with a high resolution. In practice, however, when one tries to direct an ion beam onto a desired point on the specimen surface after the specimen surface image has been observed by means of an electron beam, it is difficult to form the ion beam spot onto the desired point on the specimen surface even if the polarities of the electric signals supplied to the charged particle source and the focusing lens system are inverted. The causes of this difficulty include the deflection of the electron beam induced by leakage magnetic fields from various power supplies and the miss alignment of the optical axis of the lens system.